1. Field of the Invention
The present invention relates to a process for the manufacture of flat glass sheets with improved optical and mechanical characteristics.
In particular, the invention relates to an improvement in the transfer operation of a glass sheet strip from a molten metal tin bath to a roller annealing lehr during a process of manufacturing flat glass sheets using the "float" method, known in the art.
2. Description of the Prior Art
It is a known fact that flat glass sheets are manufactured in plants providing a first stage in which raw materials are melted and a subsequent stage in which a glass sheet is formed by floating and sliding the molten material on a tin bath. These plants, known in the art as float plants, provide an annealing lehr downstream of the molten tin bath in order to provide the glass sheet strip with required mechanical characteristics.
PCT patent application No. 92/16466 filed by the GLASSTECH company describes a float plant equipped with an annealing lehr in which a glass sheet strip travels while being supported on a fluid bed. The aim of this device is to provide an annealing process in which the glass sheet strip does not come into contact with rollers, as is the case in the conventional method, in order to improve the optical and mechanical characteristics of the glass surface itself. Thus, the glass surface at this stage still is at a high temperature and could be damaged if it comes into contact with rollers.
A main inconvenience of the above described device is the fact that it is necessary to carry out expensive modifications to existing systems, as the integral replacement of the annealing lehr which is several dozen meters long becomes necessary. Another inconvenience is that when manufacturing a new float plant, the realization of an annealing lehr having an entirely fluid bed requires high investment, and furthermore process control is difficult.